Percutaneous methods play an important role in the diagnosis and treatment of different diseases. They are based upon the principle of puncturing a pathological process through the skin. By this means, for example, tissue samples can be removed for diagnostic purposes using special biopsy needles. A treatment can also be carried out with the aid of a puncture, for example the drainage of an abscess or the thermoablation of a solitary liver metastasis. The percutaneous puncture is generally performed after a preceding imaging diagnosis by means of computer tomography (CT), magnetic resonance tomography (MRT) or ultrasound. The intervention itself can be monitored by means of imaging in real time and controlled with the aid of imaging, with CT or ultrasound currently being the imaging methods predominantly used.
Due to the minimally invasive nature, the safe access paths and the opportunities for local treatment, it is expected that percutaneous interventions will continue to increase in the next few years. Through improved diagnostics, potential pathologies can be captured at ever earlier stages and ever smaller lesions can be punctured in difficult-to-access positions, for example unclear coin-shaped lesions in the lung with dimensions between 10 and 20 mm. Percutaneous diagnostics and treatment do, however, also have some limitations. A complication rate of between 3.9% and 23.9% is reported in the literature, though the complications concerned are predominantly non-life-threatening hemorrhages, hematomas, pneumothoraces or organ injuries. Nonetheless, there is also the risk of dying from such an intervention, particularly in the event of inadvertent damage to a large vessel. A serious problem here is that of a puncture error. The rate of incorrect or incomplete punctures is reported in the literature as being up to 30%. Puncture errors can lead to a false-negative diagnosis or be the cause of an inadequate treatment dose in the desired target region. The number of puncture errors must be kept as low as possible, both in the interest of the patient and from the point of view of efficient and cost-saving medicine.
The difficulty of precise puncture lies in the variability of the target region as a result of respiratory movements, pulse-synchronous movements of organ and target region or lesion, also relative to one another, as well as possible unpredictable movements of the patient, for example caused by pain stimuli during the intervention.
Some problems can be traced to the fact that, after looking through the image recordings from the preceding imaging diagnosis and planning a suitable access path, radiologists frequently perform punctures intuitively, i.e. as a “blind puncture”. The variation in the position of a lesion as a result of respiratory activity or pulsating organ movements is estimated and included in the planning of the puncture. However, considerable scope for movement remains which almost routinely and depending also on the experience of the person performing the intervention leads to multiple puncture attempts and repeated position checks. The puncture procedure, primarily in specialized centers, is optionally monitored in real time, for example by means of x-ray or ultrasound imaging.
WO 2005/030330 A1 describes an arrangement for radiation treatment which can also be used to assist a percutaneous intervention, with an instrument being guided by a robot. To capture movements of the target region, a 4D image dataset is firstly recorded by means of markers attached to the patient externally. The target region is then marked in the individual images of the 4D image dataset so that an allocation table between the position of the externally attached markers and that of the target region located internally can finally be computed. During the intervention, the markers lying externally, and thus the patient's movements, are captured via a tracking system. By means of the allocation table, the position of the target area is determined as a function of the movement status in order in this way to be able to align the treatment instrument to the target area with greater precision.